Test apparatus and test method for testing a device under test using a multi-strobe

ABSTRACT

Provided is a test apparatus for testing a device under test, including a multi-strobe generating section that generates, for each prescribed test cycle, a multi-strobe that includes a plurality of strobes arranged at prescribed time intervals, a data detecting section that detects a logic value of a response signal output by the device under test, according to each strobe, and a data width detecting section that detects a data width indicating a period during which the logic value of the response signal matches a prescribed expected value, based on each change point of a logic value output by the data detecting section.

BACKGROUND

1. Technical Field

The present invention relates to test apparatus and a test method.

2. Related Art

A known semiconductor test apparatus measures the width (referred tohereinafter as “data width”) of an eye aperture (referred to hereinafteras the “data window”) of a response signal, which is output by a deviceunder test in response to a test signal. This semiconductor testapparatus judges the acceptability of the device under test based onwhether the data width is within a prescribed range.

The semiconductor test apparatus generates a strobe signal used tomeasure the data width, and detects leading edges and trailing edges ofthe response signal based on the strobe signal, as described in, forexample, WO 2007/091413. The data width can be measured as thedifference between a leading edge and a trailing edge of the responsesignal.

In conventional data width detecting methods, however, the leading edgesand trailing edges of the response signal are detected in different testcycles, and therefore the data width of the response signal cannot beefficiently detected. This problem has become especially prominentrecently due to an increase in the number of pins in a device undertest.

SUMMARY

Therefore, it is an object of an aspect of the innovations herein toprovide a test apparatus and a test method, which are capable ofovercoming the above drawbacks accompanying the related art. The aboveand other objects can be achieved by combinations described in theindependent claims. The dependent claims define further advantageous andexemplary combinations of the innovations herein.

According to a first aspect related to the innovations herein, oneexemplary test apparatus may include a test apparatus for testing adevice under test, comprising a multi-strobe generating section thatgenerates, for each prescribed test cycle, a multi-strobe that includesa plurality of strobes arranged at prescribed time intervals; a datadetecting section that detects a logic value of a response signal outputby the device under test, according to each strobe; and a data widthdetecting section that detects a data width indicating a period duringwhich the logic value of the response signal matches a prescribedexpected value, based on each change point of a logic value output bythe data detecting section.

According to a second aspect related to the innovations herein, oneexemplary test method may include a method for testing a device undertest, comprising generating, for each prescribed test cycle, amulti-strobe that includes a plurality of strobes arranged at prescribedtime intervals; detecting a logic value of a response signal output bythe device under test, according to each strobe; and detecting a datawidth indicating a period during which the logic value of the responsesignal matches a prescribed expected value, based on each change pointof the detected logic value.

The summary clause does not necessarily describe all necessary featuresof the embodiments of the present invention. The present invention mayalso be a sub-combination of the features described above. The above andother features and advantages of the present invention will become moreapparent from the following description of the embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary configuration of a test apparatus 100according to an embodiment of the present invention.

FIG. 2 shows a relationship between the response signal 102 andmulti-strobe signals 105.

FIG. 3 shows a relationship between the response signal 102 and themulti-strobe signal 105 when the period of the multi-strobe signal 105is longer than the data width.

FIG. 4 shows the relationship between the response signal 102 andmulti-strobe signals 105 when a single multi-strobe signal 105 is usedto detect two change points in the response signal 102.

FIG. 5 shows a detailed description of the method for detecting the datawidth.

FIG. 6 shows a method for judging acceptability of the device under test200 based on the data width measurement results.

FIG. 7 shows a method for judging acceptability of the device under test200 based on the data width measurement results.

FIG. 8 shows a relationship between the response signal 102 and amulti-strobe signal 105, according to another embodiment.

FIG. 9 shows a relationship between the response signal 102 and amulti-strobe signal 105, according to another embodiment.

FIG. 10 shows the relationship between the response signal 102 and amulti-strobe signal 105 according to another embodiment.

FIG. 11 shows a configuration of the test apparatus 100 according toanother embodiment.

FIG. 12 shows an exemplary method for detecting the jitter amount.

FIG. 13 shows a method for judging that the device under test 200 isacceptable based on the jitter amount measurement result for each pin.

FIG. 14 shows a judgment method in a case where the edge selectionsignal indicates selection of a rising edge.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, some embodiments of the present invention will bedescribed. The embodiments do not limit the invention according to theclaims, and all the combinations of the features described in theembodiments are not necessarily essential to means provided by aspectsof the invention.

FIG. 1 shows an exemplary configuration of a test apparatus 100according to an embodiment of the present invention. The test apparatus100 tests a device under test 200 such as a semiconductor circuit. Thetest apparatus 100 may be connected to a plurality of pins of the deviceunder test 200. The test apparatus 100 supplies a test signal 101 to thedevice under test 200. The device under test 200 outputs a responsesignal 102 in response to the test signal 101. The test signal 101 maybe a signal having a prescribed logic pattern, a clock signal, or thelike.

The test apparatus 100 includes a plurality of test function sections,e.g. the test function sections 20, 40, and 60 in the presentembodiment, a control section 70, a level comparator 80, a multi-strobegenerating section 82, an expected value generating section 83, and adevice window judging section 84. The test function sections 20, 40, and60 are each connected to a different output pin of the device under test200. The test apparatus 100 may include a number of test functionsections to correspond to the number of pins of the device under test200.

The test function section 20 includes a data detecting section 22, aselecting section 24, and a data width detecting section 25. The datawidth detecting section 25 includes a sequential window judging section26 and a cumulative window judging section 28. The test function section40 and the test function section 60 may both have the same configurationas the test function section 20.

The level comparator 80 compares the signal level of the response signal102 received from the device under test 200 to a prescribed thresholdvalue. The level comparator 80 may compare the signal level of theresponse signal 102 to both a relatively high-voltage threshold value VHand a relatively low-voltage threshold value VL. The level comparator 80may generate, for each threshold value, a logic data indicating thecomparison result between the signal level of the response signal 102and the threshold value, and output the generated logic data to the datadetecting section 22.

For example, the level comparator 80 outputs a logic signal 103 thatindicates “pass,” e.g. a logic value of 0, when the signal level of theresponse signal 102 is greater than the threshold value VH and thatindicates “fail,” e.g. a logic value of 1, when the signal level of theresponse signal 102 is less than the threshold value VH. The levelcomparator 80 may also output a logic signal 104 that indicates “pass,”e.g. a logic value of 0, when the signal level of the response signal102 is less than the threshold value VL and that indicates “fail,” e.g.a logic value of 1, when the signal level of the response signal 102 isgreater than the threshold value VL.

The test apparatus 100 may include a plurality of level comparators 80that correspond one-to-one with the pins of the device under test 200.Each level comparator 80 may output the logic signal 103 and the logicsignal 104 to the data detecting section 22 of the corresponding testfunction section.

The multi-strobe generating section 82 generates, for each prescribedtest cycle, a multi-strobe signal 105 that includes a plurality ofstrobe signals. For example, the multi-strobe generating section 82 maygenerate the multi-strobe signal 105 too include a plurality of strobesignals at uniform intervals.

The multi-strobe generating section 82 may generate each multi-strobesignal 105 such that the plurality of strobe signals are arranged over aperiod longer than a cycle of the response signal 102. For example, aperiod obtained by multiplying the interval between each strobe signalby the number of strobe signals in the multi-strobe signal 105 may belonger than one cycle of the response signal 102. By shortening thecycle of the response signal 102 of the device under test 200, theperiod covered by the multi-strobe signal can be made longer than thecycle of the response signal 102. More specifically, if the cycle of theresponse signal 102 is half of the test cycle, the multi-strobegenerating section 82 may generate the multi-strobe signal 105 to span aperiod longer than half of the test cycle but shorter than the full testcycle.

If the cycle of the response signal 102 is shorter than a prescribedperiod, the multi-strobe generating section 82 may generate eachmulti-strobe signal 105 such that the strobe signals are arranged over aperiod longer than a cycle of the response signal 102. For example, inresponse to a change in the frequency of the response signal 102, themulti-strobe generating section 82 may switch whether the multi-strobesignal 105 includes strobe signals arranged over a period longer orshorter than the cycle of the response signal 102.

The expected value generating section 83 outputs, to the selectingsection 24, an expected value 108 of the logic value of the responsesignal 102 received from the device under test 200. The expected valuegenerating section 83 may output the expected value 108 based on thetest signal 101.

The data detecting section 22 detects the logic value of the responsesignal 102 output by the device under test 200, according to each strobesignal. The data detecting section 22 may latch the logic signal 103 andthe logic signal 104 with the multi-strobe signal 105 output by themulti-strobe generating section 82, to generate corresponding logic data106 and logic data 107. The data detecting section 22 outputs the logicdata 106 and the logic data 107 to the selecting section 24.

The selecting section 24 selects the logic data 106 or the logic data107 based on the expected value 108 output by the expected valuegenerating section 83. The selecting section 24 outputs the selectedlogic data to the data width detecting section 25 as selected data 109.

For example, if the expected value 108 has a value of 1, the selectingsection 24 selects the logic data 106 corresponding to the high-voltagethreshold value VH. If the expected value 108 has a value of 0, theselecting section 24 selects the logic data 107 corresponding to thelow-voltage threshold value VL. Selected data 109 with a value of 0indicates a “pass” state in which the logic value of the response signal102 matches the expected value 108, and selected data 109 with a valueof 1 indicates a “fail” state in which the logic value of the responsesignal 102 does not match the expected value 108.

The data width detecting section 25 detects the data width, whichindicates the period over which the logic value of the response signal102 matches the prescribed expected value 108, based on each changepoint of the logic value output by the data detecting section 22. Thedata width detecting section 25 may detect the data width, whichindicates the period over which the logic value of the response signal102 matches the prescribed expected value 108, over the period of asingle multi-strobe signal 105, based on all of the change pointsdetected using a single multi-strobe signal 105. The data widthdetecting section 25 may detect the data width based on each changepoint of the selected data 109 output by the selecting section 24.

When a first change point at which the logic value of the responsesignal 102 changes to the expected value 108 and a second change pointat which the logic value of the response signal 102 changes from theexpected value 108 are detected with a single multi-strobe signal 105,the data width detecting section 25 detects the data width based on thepositions of the first change point and the second change point. Forexample, the data width detecting section 25 may detect the data widthbased on the positions of a first change point at which the value of theselected data 109 received from the selecting section 24 changes from 1to 0 and a second change point at which this value changes from 0 to 1.

More specifically, when a second change point at which the logic valueof the response signal 102 changes from the expected value 108 isdetected after a first change point at which the logic value of theresponse signal 102 changes to the expected value 108, with a singlemulti-strobe signal 105, the data width detecting section 25 may detectthe data width based on the positional difference between the firstchange point and the second change point. The data width detectingsection 25 may calculate the data width by using a counter to detect thephase difference between the first change point and the second changepoint.

The sequential window judging section 26 outputs, to the control section70, a sequential window judgment result 110 indicating whether thedetected data width is within a prescribed allowable range, for eachsingle multi-strobe signal 105. More specifically, the sequential windowjudging section 26 detects the data width of the response signal 102based on the first change point at which the value of the selected data109 received from the selecting section 24 changes from 1 to 0 and thesecond change point at which this value changes from 0 to 1. Thesequential window judging section 26 may judge whether the data width ofthe response signal 102 is within an acceptable range, based on the datawidth reference value 112 output by the control section 70.

The cumulative window judging section 28 outputs a cumulative windowjudgment result 114 indicating whether a phase difference between (i)the first change point having the latest phase from among the firstchange points detected with a plurality of multi-strobe signals 105 and(ii) the second change point having the earliest phase from among thesecond change points detected with a plurality of multi-strobe signals105 is within a prescribed allowable range. The cumulative windowjudging section 28 may accumulate the selected data 109 received fromthe selecting section 24 in association with each of a plurality ofstrobe signals having different phases and included in the plurality ofmulti-strobe signals 105. The cumulative window judging section 28 maydetect (i) the phase of the change point having the latest phase fromamong the first change points and (ii) the phase of the change pointhaving the earliest phase from among the second change points, based onthe accumulated comparison results.

The cumulative window judging section 28 may accumulate the selecteddata 109 in a memory, with a different address for each multi-strobesignal 105 having a different phase. The cumulative window judgingsection 28 may judge whether the data width of the response signal 102is within the allowable range based on the data width reference value112 output by the control section 70.

The test apparatus 100 may test the plurality of pins of the deviceunder test 200 in parallel. The device window judging section 84 mayjudge the acceptability of the device under test 200 based on thejudgment result by the data width detecting section 25 in each testfunction section. More specifically, the device window judging section84 acquires the cumulative window judgment result 114 corresponding toeach pin from the cumulative window judging sections 28 in the testfunction sections 20, 40, and 60.

If the judgment result output by one of the test function sections 20,40, and 60 is outside of the range of the data width reference value112, the device window judging section 84 may judge the device undertest 200 to be unacceptable. The device window judging section 84 maynotify the control section 70 concerning the judgment result.

FIG. 2 shows an exemplary method, for detecting the data width of theresponse signal 102. The detection method of the present embodimentdetects a rising change point, e.g. a leading edge, and a falling changepoint, e.g. a trailing edge, of the response signal 102 using a separatemulti-strobe signal for each type of change point. In FIG. 2, thefrequency of the response signal 102 is 1 Gbps and the data width of onecycle of the response signal 102 is 1000 ps. With these conditions, themulti-strobe generating section 82 outputs multi-strobe signals 105 thatspan a period of 600 ps around a region of the rising change point ofthe response signal 102 and the region of the falling change point ofthe response signal 102, respectively.

When detecting the rising change point of the response signal 102, themulti-strobe generating section 82 may begin outputting the multi-strobesignal 105 at a timing earlier than the timing at which the responsesignal 102 is expected to rise. When detecting the falling change pointof the response signal 102, the multi-strobe generating section 82 maybegin outputting the multi-strobe signal 105 at a timing earlier thanthe timing at which the response signal 102 is expected to fall.

FIG. 3 shows a relationship between the response signal 102 andmulti-strobe signals 105 when the frequency of the response signal 102is high and the output period of the multi-strobe signals 105 generatedby the multi-strobe generating section 82 is longer than the data width.As in FIG. 2, when detecting the rising change point of the responsesignal 102, the multi-strobe generating section 82 outputs amulti-strobe signal 105 spanning 600 ps beginning just prior to therising timing of the response signal 102. When detecting the fallingchange point of the response signal 102, the multi-strobe generatingsection 82 outputs a multi-strobe signal 105 spanning 600 ps beginningjust prior to the falling timing of the response signal 102.

However, since the frequency of the response signal 102 in FIG. 3 ishigher than the frequency of the response signal 102 in FIG. 2, themulti-strobe generating section 82 outputs the multi-strobe signal 105to span a period longer than the data width of the response signal 102.As a result, both the rising change point and the falling change pointof the response signal 102 are included within the period of a singlemulti-strobe signal 105. In this case, using a plurality of differentmulti-strobe signals 105 to detect the two change points, as describedin relation to FIG. 2, results in the same measurement being performedtwice, which decreases the efficiency of the test. Therefore, when twochange points are included within the period of one multi-strobe signal105, the test apparatus 100 desirably uses a single multi-strobe signal105 to detect the two change points of the response signal 102.

FIG. 4 shows the relationship between the response signal 102 and amulti-strobe signal 105 when a single multi-strobe signal 105 is used todetect two change points in the response signal 102. The multi-strobegenerating section 82 begins outputting the multi-strobe signal 105 justprior to a first data change point of the response signal 102, andcontinues outputting the multi-strobe signal 105 until after a seconddata change point of the response signal 102. By using a singlemulti-strobe signal 105 to detect two change points of the responsesignal 102, the test apparatus 100 can decrease the amount of timenecessary to measure the data width.

FIG. 5 shows a detailed description of the method for detecting the datawidth. The response signal 102 output by the device under test 200 has avalue that changes in response to the test signal 101 output to thedevice under test 200 by the test apparatus 100. It should be noted thatjitter occurs at the change points of the response signal 102 due tonoise or the like. The test apparatus 100 may detect the data width ofthe data window during the period when there is no jitter, and thenjudge the acceptability of the device under test 200 based on the lengthof the data width.

In the present embodiment, the multi-strobe signal 105 used to measurethe data width includes 16 strobe signals that each have differentphases. The multi-strobe generating section 82 outputs a first-phasestrobe signal at a timing just prior to the first change point of theresponse signal 102. The multi-strobe generating section 82 thensequentially generates a plurality of strobe signals that follow thefirst-phase strobe signal at constant intervals. The multi-strobegenerating section 82 generates the sixteenth-phase strobe signal afterthe second timing at which the value of the response signal 102 changes.

The selecting section 24 selects either the logic data 106 or the logicdata 107 based on the value of the expected value 108, and outputs theselected data 109 to the data width detecting section 25. When theoutput value of the level comparator 80 matches the expected value 108,the selected data 109 indicates “pass,” e.g. a logic value of 0. Whenthe output value of the level comparator 80 does not match the expectedvalue 108, the selected data 109 indicates “fail,” e.g. a logic value of1.

In the first measurement in FIG. 5, for example, the logic value of theresponse signal 102 from the first phase to the third phase of themulti-strobe signal 105 does not match the expected value 108, andtherefore the selecting section 24 outputs a value of 1. The logic valueof the response signal 102 from the fourth phase to the twelfth phase ofthe multi-strobe signal 105 matches the expected value 108, andtherefore the selecting section 24 outputs a value of 0. In the sameway, the selecting section 24 outputs a value of 1 from the thirteenthphase to the sixteenth phase of the multi-strobe signal 105.

The sequential window judging section 26 acquires the selected data 109output by the selecting section 24. The sequential window judgingsection 26 detects that the selected data 109 changes from a value of 1to a value of 0 at the fourth phase and from a value of 0 to a value of1 at the thirteenth phase. As a result, the sequential window judgingsection 26 detects the data width to have a length corresponding to ninetimes the strobe interval Ts, i.e. 9Ts.

The sequential window judging section 26 receives the data widthreference value 112 from the control section 70. The sequential windowjudging section 26 judges the acceptability of the corresponding pin ofthe device under test 200 by comparing the value of the detected datawidth to the data width reference value 112. For example, when the datawidth reference value 112 indicates a value between 5Ts and 10Ts,non-inclusive, the length corresponding to 9Ts of the multi-strobesignal 105 fulfills the condition indicated by the data width referencevalue 112. Therefore, the sequential window judging section 26 judgesthat the corresponding pin of the device under test 200 is acceptableand outputs the judgment result to the control section 70.

The test apparatus 100 can increase the accuracy of the measurement byusing a plurality of multi-strobe signals 105 to measure the responsesignal 102 multiple times. Since the timing at which the device undertest 200 outputs the response signal 102 changes, the selected data 109output by the selecting section 24 changes for each measurement. In thesecond measurement in FIG. 5, for example, the selecting section 24outputs the selected data 109 with a value of 0 from the fifth phase tothe fourteenth phase. In the third measurement, the selecting section 24outputs a value of 0 from the second phase to the eleventh phase.

While each of the multi-strobe signals 105 are being generated, thecumulative window judging section 28 may store the selected data 109output by the selecting section 24 in association with the phase of eachstrobe signal in the corresponding multi-strobe signal 105. Furthermore,the cumulative window judging section 28 may detect the leading edgephase and the trailing edge phase of the data window based on theselected data 109 output by the selecting section 24.

When measuring the leading edge phase of the data window, the cumulativewindow judging section 28 selects the latest phase at which the selecteddata 109 output by the selecting section 24 changes from a value of 1 toa value of 0, from among the phases obtained from the multiplemeasurements. For example, in the second and fifth measurements in FIG.5, the fifth phase is the latest phase at which the value of theselected data 109 changes from 1 to 0. Therefore, the cumulative windowjudging section 28 detects that the leading edge phase is the fifthphase.

In the same way, when measuring the trailing edge phase of the datawindow, the cumulative window judging section 28 selects the earliestphase at which the selected data 109 output by the selecting section 24changes from a value of 0 to a value of 1, from among the phasesobtained from the multiple measurements. For example, in the thirdmeasurement in FIG. 5, the twelfth phase is the earliest phase at whichthe value of the selected data 109 changes from 0 to 1. Therefore, thecumulative window judging section 28 detects the trailing edge phase tobe the eleventh phase, which is the phase immediately before the phaseat which the value of the selected data 109 changes from 0 to 1.

The cumulative window judging section 28 detects the data width based onthe values of the detected leading edge phase and trailing edge phase.The cumulative window judging section 28 may judge the acceptability ofthe corresponding pin by comparing the detected data width to the datawidth reference value 112.

The cumulative window judging section 28 outputs the acceptabilityjudgment result of the pin to the device window judging section 84. Thedevice window judging section 84 receives judgment results concerningthe pins of the device under test 200 corresponding to the test functionsection 20, the test function section 40, and the test function section60, respectively. The device window judging section 84 judges theacceptability of the device under test 200 based on the receivedjudgment results.

FIG. 6 shows a method for judging acceptability of the device under test200 based on the data width measurement results. The data window of theresponse signal 102 output by pin 1 has a leading edge at the fifthphase and a trailing edge at the eleventh phase. The data window of theresponse signal 102 output by pin 2 has a leading edge at the sixthphase and a trailing edge at the eleventh phase. The data window of theresponse signal 102 output by pin 3 has a leading edge at the fourthphase and a trailing edge at the tenth phase.

The data width corresponding to the phase difference between the leadingedge phase and the trailing edge phase for pins 1 to 3 is 6Ts, 5Ts, and6Ts, respectively, all of which are within the range of 5Ts to 10Tsindicated by the data width reference value 112. Since the data widthmeasurement values for all of the pins are within the reference range,the device window judging section 84 judges the device under test 200 tobe acceptable.

FIG. 7 shows a method for judging acceptability of the device under test200 based on the data width measurement results. In FIG. 7, the datawindow of the response signal 102 output by pin 2 has a leading edge atthe sixth phase and a trailing edge at the tenth phase. Accordingly, pin2 has a data width of 4Ts, which is outside of the reference range.Therefore, the device window judging section 84 judges the device undertest 200 to be unacceptable. The device window judging section 84 mayoutput the judgment result 116 to the control section 70.

In the above description, the cumulative window judging section 28judges the acceptability of each pin of the device under test 200 andthen outputs the cumulative window judgment result 114 to the devicewindow judging section 84, but the cumulative window judging section 28may instead output the detected data width to the device window judgingsection 84. In this case, the device window judging section 84 may judgethe acceptability of the device under test 200 based on (i) the value ofthe data width output by the cumulative window judging section 28 ineach test function section and (ii) the data width reference value 112output by the control section 70.

As described above, the test apparatus 100 can accurately detect thedata width of the response signal 102 by accumulating the selected data109 in association with the phases of the plurality of strobe signalsincluded in each of the plurality of multi-strobe signals 105.Furthermore, the test apparatus 100 can judge the acceptability of thedevice under test 200 in a short time by testing the pins of the deviceunder test 200 in parallel.

FIG. 8 shows a relationship between the response signal 102 and amulti-strobe signal 105, according to another embodiment. In FIG. 8, theperiod during which the multi-strobe generating section 82 generates themulti-strobe signal 105 does not include a second change point where thelogic value of the response signal 102 changes from the expected value108. If a second change point at which the logic value of the responsesignal 102 changes from the expected value 108 is not detected after afirst change point at which the logic value of the response signal 102changes to the expected value 108 is detected in a single multi-strobesignal 105, the multi-strobe generating section 82 may adjust the phaseof the multi-strobe signal 105 until a second change point at which thelogic value of the response signal 102 changes from the expected value108 is detected after a first change point at which the logic value ofthe response signal 102 changes to the expected value 108 is detected.For example, the multi-strobe generating section 82 may adjust the phaseof the multi-strobe signal 105 to have a position shown by the strobesignal after position adjustment shown in FIG. 8.

If a second change point at which the logic value of the response signal102 changes from the expected value 108 is not detected after a firstchange point at which the logic value of the response signal 102 changesto the expected value 108 is detected, with a single multi-strobe signal105, the data width detecting section 25 may detect the data width basedon the period from the first change point to the end point of themulti-strobe signal 105. For example, if the multi-strobe signal 105 isat the position of the strobe signal before position adjustment shown inFIG. 8, the data width detecting section 25 may detect the data width tobe the period between the first change point and the strobe signalhaving the latest phase in the strobe signal before position adjustment.

If a second change point at which the logic value of the response signal102 changes from the expected value 108 is not detected after a firstchange point at which the logic value of the response signal 102 changesto the expected value 108 is detected, with a single multi-strobe signal105, the multi-strobe generating section 82 may delay the phase of themulti-strobe signal 105 on a condition that the data width detected bythe data width detecting section 25 is outside of the prescribedallowable range. For example, if the multi-strobe signal 105 is at theposition of the strobe signal before position adjustment shown in FIG. 8and the data width detected by the data width detecting section 25 isnot within the range of the data width reference value 112, themulti-strobe generating section 82 may delay the phase of themulti-strobe signal 105 such that the multi-strobe signal 105 is at theposition of the strobe signal after position adjustment.

When the data width detected by the data width detecting section 25 isnot within the range of the data width reference value 112, themulti-strobe generating section 82 may change the phase of themulti-strobe signal 105. The multi-strobe generating section 82 maydetermine whether to change the phase of the multi-strobe signal 105based on the judgment result from the sequential window judging section26. Instead, the multi-strobe generating section 82 may determinewhether to change the phase of the multi-strobe signal 105 under controlof the control section 70.

FIG. 9 shows a relationship between the response signal 102 and amulti-strobe signal 105, according to another embodiment. If a firstchange point at which the logic value of the response signal 102 changesto the expected value 108 is not detected before a second change pointat which the logic value of the response signal 102 changes from theexpected value 108 is detected, with a single multi-strobe signal 105,the data width detecting section 25 may detect the data width to be theperiod from the start point of the multi-strobe signal 105 to the secondchange point. For example, if the multi-strobe signal 105 is at theposition of the strobe signal before position adjustment shown in FIG.9, the data width detecting section 25 may detect the data width to bethe period between (i) the strobe signal having the earliest phase inthe strobe signal before position adjustment and (ii) the second changepoint.

If a first change point at which the logic value of the response signal102 changes to the expected value 108 is not detected before a secondchange point at which the logic value of the response signal 102 changesfrom the expected value 108 is detected, with a single multi-strobesignal 105, the multi-strobe generating section 82 may cause the phaseof the multi-strobe signal 105 to be earlier on a condition that thedata width detected by the data width detecting section 25 is outside ofthe prescribed allowable range. For example, if the multi-strobe signal105 is at the position of the strobe signal before position adjustmentshown in FIG. 9 and the data width detected by the data width detectingsection 25 is not within the range of the data width reference value112, the multi-strobe generating section 82 may cause the phase of themulti-strobe signal 105 to be earlier such that the multi-strobe signal105 is at the position of the strobe signal after position adjustment.If the data width detected by the data width detecting section 25 iswithin the range of the data width reference value 112, the multi-strobegenerating section 82 need not change the phase of the multi-strobesignal 105.

FIG. 10 shows the relationship between the response signal 102 and amulti-strobe signal 105 according to another embodiment. The presentembodiment describes a situation where the multi-strobe generatingsection detects a first change point at which the logic value of theresponse signal 102 changes to the expected value 108 after detecting asecond change point at which the logic value of the response signal 102changes from the expected value 108, with a single multi-strobe signal105. In this case, the multi-strobe generating section 82 may change thephase of the multi-strobe signal 105 until the data width detected bythe data width detecting section 25 is within the prescribed allowablerange. The multi-strobe generating section 82 may cause the phase of themulti-strobe signal 105 to be earlier such that the multi-strobe signal105 is at the position of the strobe signal 1 after position adjustmentshown in FIG. 10, or may delay the phase of the multi-strobe signal 105such that the multi-strobe signal 105 is at the position of the strobesignal 2 after position adjustment shown in FIG. 10.

FIG. 11 shows a configuration of the test apparatus 100 according toanother embodiment. The test apparatus 100 of the present embodiment isfurther provided with a device jitter judging section 86. The testfunction section 20 further includes a jitter detecting section 29. Thejitter detecting section 29 detects the jitter of the first change pointor the second change point for each multi-strobe signal.

The jitter detecting section 29 includes a sequential jitter judgingsection 30 that outputs a sequential jitter judgment result indicatingwhether the detected jitter is within an allowable range, for eachmulti-strobe signal 105. The jitter detecting section 29 also includes acumulative jitter judging section 32 that outputs a cumulative jitterjudgment result 120 indicating whether a phase difference between thelatest phase and the earliest phase, from among the phases of the changepoints detected with a plurality of multi-strobe signals 105, is withinthe prescribed allowable range. The control section 70 outputs, to thesequential jitter judging section 30 and the cumulative jitter judgingsection 32, a jitter amount reference value 122 and an edge selectionsignal 124 that selects a polarity of the change point of the selecteddata 109 for which jitter is to be measured.

The test apparatus 100 may test the plurality of pins of the deviceunder test 200 in parallel. A jitter detecting section 29 is providedfor each pin of the device under test 200, and the test apparatus 100may include a device jitter judging section 86 that judges theacceptability of the device under test 200 based on the judgment resultsfrom the plurality of jitter detecting sections 29. In other words, inthe same manner as the test function section 20, the test functionsection 40 and the test function section 60 may each include a jitterdetecting section 29, and the device jitter judging section 86 may judgethe acceptability of the device under test 200 based on the judgmentresults output by the test function sections 20, 40, and 60.

The sequential jitter judging section 30 acquires the selected data 109obtained as a result of the multiple measurements by the selectingsection 24. The sequential jitter judging section 30 detects a phaserange of the multi-strobe signal 105 in which jitter occurs, based onthe selected data 109. When the edge selection signal 124 has a value of1, the sequential jitter judging section 30 may measure the amount ofjitter at a timing at which the value of the selected data 109 changesfrom 1 to 0. When the edge selection signal 124 has a value of 0, thesequential jitter judging section 30 may measure the amount of jitter ata timing at which the value of the selected data 109 changes from 0 to1.

When the measured jitter amount is within the range indicated by thejitter amount reference value 122, the sequential jitter judging section30 outputs a cumulative jitter judgment result 120 indicating that themeasured pin is acceptable to the control section 70. On the other hand,when the measured jitter amount is outside the range indicated by thejitter amount reference value 122, the sequential jitter judging section30 outputs a cumulative jitter judgment result 120 indicating that themeasured pin is unacceptable to the control section 70.

The cumulative jitter judging section 32 accumulates the selected data109 obtained by the selecting section 24 over multiple measurements, inassociation with the phase of each strobe signal in the multi-strobesignal 105. The cumulative jitter judging section 32 detects the jitteramount based on the accumulated selected data 109. The cumulative jitterjudging section 32 may judge the acceptability of the jitter amount ofthe corresponding pin based on the jitter amount reference value 122output by the control section 70.

The device jitter judging section 86 acquires a cumulative jitterjudgment result 126 for each pin output by the corresponding testfunction sections 20, 40 and 60. The device jitter judging section 86judges the acceptability of the device under test 200 based on thecumulative jitter judgment result 126 acquired for each pin. The devicejitter judging section 86 may notify the control section 70 concerningthe judgment result.

FIG. 12 shows an exemplary method for detecting the jitter amount. Theselected data 109 and each signal in FIG. 12 may be the same as thoseshown in FIG. 5. The cumulative jitter judging section 32 detects theleading edge and the trailing edge in the phase range of themulti-strobe signal 105 in which jitter occurs, based on the selecteddata 109 shown in FIG. 12.

In FIG. 12, the timing of a falling change point at which the value ofthe selected data 109 changes from 1 to 0 is the fourth phase, the fifthphase, the second phase, the fourth phase, and the fifth phase,respectively, in the first measurement to the fifth measurement.Therefore, the cumulative jitter judging section 32 detects that thevalue of the selected data 109 changes from 1 to 0 in a range betweenthe second phase and the fourth phase. In other words, the leading edgephase of the jitter (J1 in FIG. 12) when the value of the selected data109 changes from 1 to 0 is the second phase and the trailing edge phaseof this jitter (J2 in FIG. 12) is the fourth phase. Therefore, thecumulative jitter judging section 32 detects the jitter amount to be3Ts.

In the same way, the timing of a rising change point at which the valueof the selected data 109 changes from 0 to 1 is the thirteenth phase,the fifteenth phase, the twelfth phase, the fifteenth phase, and thefourteenth phase, respectively, in the first measurement to the fifthmeasurement. Therefore, the cumulative jitter judging section 32 detectsthat the value of the selected data 109 changes from 0 to 1 in a rangebetween the twelfth phase and the fifteenth phase. In other words, theleading edge phase of the jitter (J3 in FIG. 12) when the value of theselected data 109 changes from 0 to 1 is the twelfth phase and thetrailing edge phase of this jitter (J4 in FIG. 12) is the fifteenthphase. Therefore, the cumulative jitter judging section 32 detects thejitter amount to be 3Ts.

FIG. 13 shows a method for judging that the device under test 200 isacceptable based on the jitter amount measurement result for each pin.For pin 1, the leading edge phase 31 and the trailing edge phase J2 ofthe jitter of the falling edge are the second phase and the fourthphase, respectively, and so the jitter amount is 3Ts. In the same way,the jitter amounts of the falling edges for pin 2 and pin 3 are both4Ts. On the other hand, the jitter amount of the rising edge is 3Ts,3Ts, and 5Ts, respectively, for pins 1 to 3.

In FIG. 13, the minimum value of the jitter amount reference value 122is 1Ts and the maximum value is 4Ts. The edge selection signal 124output to the cumulative jitter judging section 32 by the controlsection 70 indicates selection of a falling edge. Therefore, eachcumulative jitter judging section 32 in the test function sections 20,40, and 60 compares the jitter amount of the falling edge for thecorresponding pin to the value indicated by the jitter amount referencevalue 122.

In FIG. 13, the jitter amount of the falling edge for pins 1 to 3 iswithin the range of the jitter amount reference value 122, and thereforeeach cumulative jitter judging section 32 judges the corresponding pinto be acceptable. The device jitter judging section 86 judges that thedevice under test 200 is acceptable based on the cumulative jitterjudgment result 126 output by each cumulative jitter judging section 32in the test function sections 20, 40, and 60.

FIG. 14 shows a method for judging that the device under test 200 isunacceptable based on the jitter amount measurement result for each pin.In FIG. 14, the jitter amount for each pin is the same as in FIG. 13.However, FIG. 14 differs from FIG. 13 in that the edge selection signal124 indicates selection of a rising edge. Therefore, each cumulativejitter judging section 32 in the test function sections 20, 40, and 60judges the acceptability of the corresponding pin based on the jitteramount of the rising edge.

At the rising edge, the jitter amount of the output data from pin 3 is5Ts, which exceeds the maximum value for the reference jitter of 4Ts.Accordingly, the cumulative jitter judging section 32 in the testfunction section 60 corresponding to pin 3 judges that pin 3 isunacceptable. The device jitter judging section 86 may judge the deviceunder test 200 to be unacceptable based on the cumulative jitterjudgment result 126 output by the cumulative jitter judging section 32in the test function section 60.

In the above description, the cumulative jitter judging section 32judges the acceptability of each pin of the device under test 200 andthen outputs the cumulative jitter judgment result 126 to the devicejitter judging section 86, but the cumulative jitter judging section 32may instead output the value of the detected data width to the devicejitter judging section 86. In this case, the device jitter judgingsection 86 may judge the acceptability of the device under test 200based on (i) the value of the jitter amount output by each cumulativejitter judging section 32 in the test function sections 20, 40, and 60and (ii) the jitter amount reference value 122 output by the controlsection 70. The device jitter judging section 86 may output the judgmentresult 128 to the control section 70.

As described above, the test apparatus 100 can accurately detect thejitter amount of the response signal 102 by accumulating the selecteddata 109 in association with the phases of the strobe signals in each ofthe plurality of multi-strobe signals 105. The test apparatus 100 canjudge the acceptability of the device under test 200 in a short time bytesting the pins of the device under test 200 in parallel.

While the embodiments of the present invention have been described, thetechnical scope of the invention is not limited to the above describedembodiments. It is apparent to persons skilled in the art that variousalterations and improvements can be added to the above-describedembodiments. It is also apparent from the scope of the claims that theembodiments added with such alterations or improvements can be includedin the technical scope of the invention.

The operations, procedures, steps, and stages of each process performedby an apparatus, system, program, and method shown in the claims,embodiments, or diagrams can be performed in any order as long as theorder is not indicated by “prior to,” “before,” or the like and as longas the output from a previous process is not used in a later process.Even if the process flow is described using phrases such as “first” or“next” in the claims, embodiments, or diagrams, it does not necessarilymean that the process must be performed in this order.

As made clear from the above, the embodiments of the present inventioncan be used to realize a test apparatus and a test method for decreasingthe amount of time necessary to test for jitter amount or data width.

1. A test apparatus for testing a device under test, comprising: amulti-strobe generating section that generates, for each prescribed testcycle, a multi-strobe that includes a plurality of strobes arranged atprescribed time intervals; a data detecting section that detects a logicvalue of a response signal output by the device under test, according toeach strobe; and a period detecting section that detects a matchingperiod during which the logic value of the response signal matches aprescribed expected value, based on each change point of a logic valueoutput by the data detecting section, wherein when (i) a first changepoint at which the logic value of the response signal changes to theexpected value and (ii) a second change point at which the logic valueof the response signal changes from the expected value are detected witha single multi-strobe, the period detecting section detects the matchingperiod based on positions of the first change point and the secondchange point, and when (i) a second change point at which the logicvalue of the response signal changes from the expected value is notdetected after (ii) a first change point at which the logic value of theresponse signal changes to the expected value is detected, with a singlemulti-strobe, the multi-strobe generating section adjusts the positionof the multi-strobe until a second change point at which the logic valueof the response signal changes from the expected value is detected afterthe first change point at which the logic value of the response signalchanges to the expected value is detected.
 2. The test apparatusaccording to claim 1, wherein the multi-strobe generating sectiongenerates each multi-strobe such that the plurality of strobes in themulti-strobe are arranged over a period longer than a cycle of theresponse signal.
 3. The test apparatus according to claim 1, whereinwhen (i) a second change point at which the logic value of the responsesignal changes from the expected value is detected after (ii) a firstchange point at which the logic value of the response signal changes tothe expected value is detected, with a single multi-strobe, the perioddetecting section detects the matching period based on a phasedifference between the first change point and the second change point.4. The test apparatus according to claim 1, wherein the period detectingsection includes: a sequential window judging section that, for eachmulti-strobe, outputs a sequential window judgment result indicatingwhether the detected matching period is within the prescribed allowablerange; and a cumulative window judging section that outputs a cumulativewindow judgment result indicating whether a phase difference between (i)a first change point having a latest phase from among the first changepoints detected by a plurality of the multi-strobes and (ii) a secondchange point having an earliest phase from among the second changepoints detected by a plurality of multi-strobes is within an allowablerange.
 5. The test apparatus according to claim 1, wherein the testapparatus tests a plurality of pins of the device under test inparallel, one period detecting section is provided for each pin of thedevice under test, and the test apparatus further comprises a devicewindow judging section that judges acceptability of the device undertest based on a judgment result from each period detecting section. 6.The test apparatus according to claim 1, further comprising a jitterdetecting section that detects jitter of the first change point or thesecond change point in each multi-strobe.
 7. The test apparatusaccording to claim 6, wherein the jitter detecting section includes: asequential jitter judging section that, for each multi-strobe, outputs asequential jitter judgment result indicating whether the detected jitteris within an allowable range; and a cumulative jitter judging sectionthat outputs a cumulative jitter judgment result indicating whether aphase difference between (i) a latest phase from among phases of thechange points detected by a plurality of the multi-strobes and (ii) anearliest phase from among the phases of the change points detected by aplurality of the multi-strobes is within an allowable range.
 8. The testapparatus according to claim 7, wherein the test apparatus tests aplurality of pins of the device under test in parallel, one jitterdetecting section is provided for each pin of the device under test, andthe test apparatus further comprises a device jitter judging sectionthat judges acceptability of the device under test based on a judgmentresult from each jitter detecting section.
 9. The test apparatusaccording to claim 5, wherein when (i) a first change point at which thelogic value of the response signal changes from the expected value isdetected after (ii) a second change point at which the logic value ofthe response signal changes to the expected value is detected, with asingle multi-strobe, the multi-strobe generating section adjusts theposition of the multi-strobe until the second change point at which thelogic value of the response signal changes from the expected value isdetected after another first change point at which the logic value ofthe response signal changes to the expected value is detected.
 10. Thetest apparatus according to claim 1, wherein when (i) a first changepoint at which the logic value of the response signal changes from theexpected value is detected after (ii) a second change point at which thelogic value of the response signal changes to the expected value isdetected, with a single multi-strobe, the multi-strobe generatingsection adjusts the position of the multi-strobe until another secondchange point at which the logic value of the response signal changesfrom the expected value is detected after the first change point atwhich the logic value of the response signal changes to the expectedvalue is detected.
 11. A test apparatus for testing a device under test,comprising: a multi-strobe generating section that generates, for eachprescribed test cycle, a multi-strobe that includes a plurality ofstrobes arranged at prescribed time intervals; a data detecting sectionthat detects a logic value of a response signal output by the deviceunder test, according to each strobe; and a period detecting sectionthat detects a matching period during which the logic value of theresponse signal matches a prescribed expected value, based on eachchange point of a logic value output by the data detecting section,wherein when (i) a first change point at which the logic value of theresponse signal changes to the expected value and (ii) a second changepoint at which the logic value of the response signal changes from theexpected value are detected with a single multi-strobe, the perioddetecting section detects the matching period based on positions of thefirst change point and the second change point, and when (i) a firstchange point at which the logic value of the response signal changes tothe expected value is not detected before (ii) a second change point atwhich the logic value of the response signal changes from the expectedvalue is detected, with a single multi-strobe, the period detectingsection detects the matching period based on a period from a start pointof the multi-strobe to the second change point.
 12. The test apparatusaccording to claim 11, wherein when (i) a second change point at whichthe logic value of the response signal changes from the expected valueis not detected after (ii) a first change point at which the logic valueof the response signal changes to the expected value is detected, with asingle multi-strobe, the period detecting section detects the matchingperiod based on a period from the first change point to an end point ofthe multi-strobe.
 13. The test apparatus according to claim 12, whereinwhen (i) a second change point at which the logic value of the responsesignal changes from the expected value is not detected after (ii) afirst change point at which the logic value of the response signalchanges to the expected value is detected, with a single multi-strobe,the multi-strobe generating section delays the phase of themulti-strobe, on a condition that the matching period detected by theperiod detecting section is outside of a prescribed allowable range. 14.The test apparatus according to claim 11, wherein when (i) a firstchange point at which the logic value of the response signal changes tothe expected value is not detected before (ii) a second change point atwhich the logic value of the response signal changes from the expectedvalue is detected, with a single multi-strobe, the multi-strobegenerating section causes the phase of the multi-strobe to be earlier,on a condition that the matching period detected by the period detectingsection is outside of a prescribed allowable range.
 15. A method fortesting a device under test, comprising: generating, for each prescribedtest cycle, a multi-strobe that includes a plurality of strobes arrangedat prescribed time intervals; detecting a logic value of a responsesignal output by the device under test, according to each strobe; anddetecting a matching period indicating a period during which the logicvalue of the response signal matches a prescribed expected value, basedon each change point of the detected logic value, wherein when (i) afirst change point at which the logic value of the response signalchanges to the expected value and (ii) a second change point at whichthe logic value of the response signal changes from the expected valueare detected with a single multi-strobe, the matching period is detectedbased on positions of the first change point and the second changepoint, and when (i) a second change point at which the logic value ofthe response signal changes from the expected value is not detectedafter (ii) a first change point at which the logic value of the responsesignal changes to the expected value is detected, with a singlemulti-strobe, the position of the multi-strobe is adjusted until asecond change point at which the logic value of the response signalchanges from the expected value is detected after the first chancrepoint at which the logic value of the response signal changes to theexpected value is detected.
 16. The method according to claim 15,wherein when (i) a first change point at which the logic value of theresponse signal changes to the expected value is not detected before(ii) a second change point at which the logic value of the responsesignal changes from the expected value is detected, with a singlemulti-strobe, the position of the multi-strobe is adjusted until thesecond change point at which the logic value of the response signalchanges from the expected value is detected after a first change pointat which the logic value of the response signal changes to the expectedvalue is detected.
 17. The method according to claim 15, wherein when(i) a first change point at which the logic value of the response signalchanges from the expected value is detected after (ii) a second changepoint at which the logic value of the response signal changes to theexpected value is detected, with a single multi-strobe, the position ofthe multi-strobe is adjusted until the second change point at which thelogic value of the response signal changes from the expected value isdetected after another first change point at which the logic value ofthe response signal changes to the expected value is detected.
 18. Themethod according to claim 15, wherein when (i) a first change point atwhich the logic value of the response signal changes from the expectedvalue is detected after (ii) a second change point at which the logicvalue of the response signal changes to the expected value is detected,with a single multi-strobe, the position of the multi-strobe is adjusteduntil another second change point at which the logic value of theresponse signal changes from the expected value is detected after thefirst change point at which the logic value of the response signalchanges to the expected value is detected.
 19. A method for testing adevice under test, comprising: generating, for each prescribed testcycle, a multi-strobe that includes a plurality of strobes arranged atprescribed time intervals; detecting a logic value of a response signaloutput by the device under test, according to each strobe; and detectinga matching period indicating a period during which the logic value ofthe response signal matches a prescribed expected value, based on eachchange point of the detected logic value, wherein when (i) a firstchange point at which the logic value of the response signal changes tothe expected value and (ii) a second change point at which the logicvalue of the response signal changes from the expected value aredetected with a single multi-strobe, the matching period is detectedbased on positions of the first change point and the second changepoint, and when (i) a first change point at which the logic value of theresponse signal changes to the expected value is not detected before(ii) a second change point at which the logic value of the responsesignal changes from the expected value is detected, with a singlemulti-strobe, the matching period is detected based on a period from astart point of the multi-strobe to the second change point.
 20. The testapparatus according to claim 1, wherein when (i) a first change point atwhich the logic value of the response signal changes to the expectedvalue is not detected before (ii) a second change point at which thelogic value of the response signal changes from the expected value isdetected, with a single multi-strobe, the multi-strobe generatingsection adjusts the position of the multi-strobe until the second changepoint at which the logic value of the response signal changes from theexpected value is detected after a first change point at which the logicvalue of the response signal changes to the expected value is detected.